The world is about to find out, at long last, what it means to cross President Barack Obama’s “red line” on the use of chemical weapons.

As Secretary of State John Kerry made clear, the U.S. is now convinced that Syrian dictator Bashar Assad used rockets armed with chemical agents to kill civilians near Damascus. Estimates of 1,000 or more deaths in the attacks, accompanied by photographs and video of bodies — many of them children — shrouded in white cloth shocked the world.

A year ago, Obama warned of a “red line” that, if crossed, would change what had been effectively a hands-off U.S. posture. Tragically, last week’s chemical attack was not Assad’s first time crossing that red line — only his latest and apparently his deadliest. Assad, with Russia and Iran at his back, clearly does not respect U.S. might and the world’s resolve.

It’s time that he did.

Like the Obama administration, this newspaper has been cautious in approaching Syria, recognizing the geopolitical implications of U.S. involvement in an internal uprising against Assad. We’ve also considered a war-weary American public reluctant to see sons and daughters deployed to another distant conflict.

Yet all diplomatic avenues have failed. Now it falls to the world’s superpower to punish a regime that violates all semblance of international law by employing rockets loaded with chemical warheads. No civilized nation could — or should — sanction such behavior, especially when directed at a country’s own citizens.

The Obama administration has signaled its intent to fire missiles from destroyers at sea or long-range bombers in a brief, intense strike. The plan is to deliver a message of condemnation while minimizing U.S. involvement beyond this mission.

It’s a worthy goal, and we would hope the world would speak with one clear voice to echo Kerry, who correctly railed against the Assad regime’s “moral obscenity” that “defies any code of morality.” Russia’s expected veto makes U.N. Security Council action unlikely, but the U.S. would be wise to recruit the European Union, Arab League and NATO allies into a broad military coalition.

Americans must hope that Obama’s action plan also includes extensive consideration of the risk that goes with the goal. Hezbollah fighters are on the ground in Syria. Will Iran and, ultimately, Russia stand silent after their ally and protectorate is bombed?

And no matter how surgical the strikes or how military the targets, civilian casualties are unavoidable when bombs fall. The U.S. and its allies have a duty to act, but the world must not forget that actions have consequences.

What should U.S. target?

Some options for a strike on Syria:

Target the Syrian army’s stores of chemical weapons, more than 1,000 tons, with “agent-defeat” bombs that first shred containers in a rain of metal darts and then incinerate the chemicals with white phosphorus. Problem: The chemicals are likely to be on the move in anticipation of a strike.

Hit the headquarters, air bases and arms depots of the regime’s elite Republican Guard and particularly Maher Assad’s Fourth Armored Division, which reportedly carried out last week’s attack. However, fewer tanks, helicopters or jets can be destroyed by a single cruise missile (unit cost: $1.5 million).

A more widespread, scattershot approach, aiming to “degrade” WMD stockpiles.

Take aim at dictator Bashar Assad and any of his relatives with a claim on political power — plus all political symbols of family power, including residences. This, says Wall Street Journal columnist Bret Stephens, is the one option that has a chance to pay strategic dividends from a symbolic action.

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